The present invention has been developed for use in twin screw mixing-compounding machines of the type used in the plastics industry, for example, and illustrated in the present assignee's prior U.S. Pat. Nos. 3,195,868 and 4,826,323. The larger machines of this type utilize preferably hydraulic motor-driven shafts with radially mating co-wiping, individual paddles, or worm sections thereon, both of which, hereinafter, are to be included within the term "paddle", as used hereinafter. In machines of this character, the shafts which mount the paddles must be rotated at the same speed, and in the same direction of rotation, in order for the paddles to completely co-wipe one another, and, at the same time, completely wipe the interior of the barrel bore in which they are operative. Whether the paddle employed is of the single or multi-lobe type, the geometry of the surface of one of the paddle components must be generated by the mating paddle component for co-wiping to occur, and these geometric forms are a direct function of barrel bore diameter to shaft center-to-center distance. Normally, to increase the power supplied to the paddles of such machines for mixing purposes and increased output, it is necessary to increase the dimensions of both the paddles and the shafts which drive them, to carry the increased loads at acceptable stress levels. However, to increase shaft diameter for a machine having a given size barrel, it is necessary to alter the bore to center-to-center distance ratio of the twin screw-paddle assembly, which adds to its width. The paddle component wall thickness, accordingly, increases in relationship to the increased shaft diameter and, with thicker paddle elements, the open volume of the machine for the same bore diameter is significantly decreased. Thus, present day machines which are to produce an increased rate of processing product cannot tolerate the power increases which are necessary for processing the materials.
Typically, today, involute gear teeth splines are used to transfer the power from the shafts to the paddles, as disclosed in prior U.S. Pat. No. 4,591,487, but various keys, and hexagonal shaft configurations, have also been proposed. While all are not considered germane to the field of the present invention, applicants are aware of the following prior patents, which they incorporate herein by reference:
U.S. Pat. No. 2,668,756 Carney PA1 U.S. Pat. No. 2,777,353 Willis PA1 U.S. Pat. No. 3,584,667 Reiland PA1 U.S. Pat. No. 4,073,013 Blach PA1 U.S. Pat. No. 4,236,833 Blach PA1 U.S. Pat. No. 4,269,246 Larson et al PA1 U.S. Pat. No. 4,591,487 Fritsch PA1 U.S. Pat. No. 5,171,117 Seidl